.backtop {
    display: none;
    position: fixed;
    left: 50%;
    bottom: 88px;
    width: 28px;
    height: 46px;
    margin-left: 630px;
    background: url(../images/backtop.png) no-repeat 0 0;
}

.backtop:hover {
    background-position: -38px 0;
}

